People sometimes quip that children who have a tough time growing up are old beyond their years. New research, however, suggests that could be literally true: children who have suffered violence at a young age, it appears, actually suffer from premature ageing of their DNA.

At the end of all the chromosomes found in our body are strands of DNA called telomeres. Their sole purpose is to keep the chromosomes—which are coiled strands of DNA themselves—from unravelling. You can think of them as the plastic tips on the end of your shoe laces.

Each time a cell divides, the telomeres chain gets shorter, which puts a limit on how many times a cell can continue to divide. It's no surprise, then, that a glut of recent studies closely link the shortening of telomeres with ageing—in fact, they seem to connect physical stresses to biological age. Smoking, drinking and obesity all accelerate the shortening of telomeres, for instance.

The study, published in Molecular Psychiatry, uses a data set collected from 1,100 families with twins, who have been followed from birth and are now 18. Through DNA testing and interviews which reveal differing histories of exposure to violence in the children—be it domestic violence, frequent bullying or some other physical maltreatment—the researchers have been able to investigate the link between the two.

They've found that those children with a history of two or more kinds of violent exposures in their past have significantly more telomeres loss than other children. Because shorter telomeres are linked with shorter lifespans and greater chances of suffering from chronic disease, the message couldn't be clearer. Terrie Moffitt, one of the researchers, explains to Medical Express:

"An ounce of prevention is worth a pound of cure. Some of the billions of dollars spent on diseases of aging such as diabetes, heart disease and dementia might be better invested in protecting children from harm."

The findings suggest that cumulative childhood stress is linked to accelerated ageing—which seems to suggest that the concept of children being old before their years is, painfully, all too true. [Molecular Psychiatry via Medical Express]